Recent developments in the ever-demanding field of construction industry have evolved into the investigation of highly flowable concrete (HFC). Mix formulation on the HFC is complex and depends on the relationship between various potential constituents in the mix. In the past decades, green materials have been considered as one of the ingredients in HFC. This effort is motivated mainly by the limitation of landfill area and the intention to reduce the greenhouse effects. Even though there is incorporation of green material in conventional concrete, the fundamentals on the rheological and mechanical properties of HFC incorporating new green cementitious materials are still open and require attention. This research aims to evaluate the rheological and mechanical properties of HFC containing green materials such as eggshells and ground granulated blast-furnace slag (GGBS). In this study, experimental techniques for obtaining the properties of the HFC were performed. The effect of mix imparting on the requested fluidity and segregation resistance were evaluated. To assess the compressive and split-tensile strengths of HFC, concrete cubes (100 × 100 × 100 mm) were tested under compression, and cylindrical specimens (50 mm diameter × 100 mm height) were tested for split-tensile strength after 7 and 28 days of water curing. The failure behavior of the test specimens was then observed. The results of the experiments demonstrated that all HFC combinations containing eggshells and GGBS met the EFNARC standards for fresh properties. The compressive strength of HFC with ESP and GGBS attained the ultimate strength at volume fractions of 15% and 30%, respectively. The results and observations from the present study also indicate that incorporating recycled Ground Granulated Blast Furnace Slag (GGBS) provides a notable advantage in both the mechanical properties of HFC and its failure behavioral pattern when used as a partial replacement for cement.